Fixing Device and Image Forming System Using the Same

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2024-153463 filed Sep. 5, 2024.

The present disclosure relates to a fixing device and an image forming system using the same.

4 FIG. As an example of a fixing device of the related art, the fixing device disclosed in Japanese Patent No. 5386904 (exemplary embodiment and) is known.

If an endless fixing belt is sandwiched and pressurized immediately after being heated, wrinkles are likely to occur. This publication discloses an image forming apparatus including a fixing device that addresses this issue. In this fixing device, before the endless fixing belt is heated, it is rotated in the reverse direction, and after it is heated, it is rotated in the forward direction, so as to prolong the time before the heated portion of the endless fixing belt is pressurized, thereby reducing the occurrence of wrinkles.

Aspects of non-limiting embodiments of the present disclosure relate to a fixing device and an image forming system using the same in which, at the time of fixing an unfixed image on a medium by heating and pressurizing a belt-like transport fixing unit and then by cooling it, the transport fixing unit is driven to perform idling rotation while suppressing a temperature drop of a heated portion of the transport fixing unit and a heating fixing unit during a standby mode in which power supply to the heating fixing unit is interrupted or reduced.

Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above.

According to an aspect of the present disclosure, there is provided a fixing device including: a heating fixing unit that is rotatable and includes a heat source; a belt-like transport fixing unit that is rotatably provided as a result of being tightly stretched on the heating fixing unit and that transports a medium having an unfixed image formed thereon while contacting a surface of the medium on which the unfixed image is formed; a pressurizing fixing unit that is rotatable and is disposed to face the heating fixing unit so as to sandwich the transport fixing unit therebetween and that applies pressure so as to form a fixing area between the pressurizing fixing unit and the heating fixing unit, the fixing area being an area where the unfixed image is fixed; a cooling unit that cools the transport fixing unit, the cooling unit being disposed in a transport region of the transport fixing unit for the medium so as to contact a back side of the transport fixing unit, the cooling unit being disposed at a position farther downstream than the fixing area in a transport direction of the medium; and a driving controller that executes drive control during a standby mode to cause the transport fixing unit to perform idling rotation to repeat a forward rotation operation and a reverse rotation operation so that a portion of the transport fixing unit including a contact area where the transport fixing unit contacts the heating fixing unit and an area of the transport fixing unit which has been heated by the heating fixing unit and which has not yet reached a cooling area of the cooling unit contacts the heating fixing unit, the standby mode being a mode in which power supply to the heat source of the heating fixing unit is interrupted or reduced.

1 FIG.A illustrates an overview of an image forming system including a fixing device which incorporates an exemplary embodiment of the disclosure.

1 FIG.A 11 10 11 10 The image forming system shown inincludes an image forming unitand a fixing device. The image forming unitforms an image G, which is not yet fixed (hereinafter such an image will be called an unfixed image G), on a medium S. The fixing devicefixes the unfixed image G formed on the medium S.

10 10 1 2 3 4 6 1 1 2 1 3 1 2 3 3 1 4 2 4 2 2 4 1 1 6 2 2 1 2 1 4 1 a a In this example, the fixing deviceheats and pressurizes the medium S having the unfixed image G held thereon and then cools it so as to fix the unfixed image G onto the medium S. The fixing deviceincludes a heating fixing unit, a belt-like transport fixing unit, a pressurizing fixing unit, a cooling unit, and a driving controller. The heating fixing unitis rotatable and includes a heat source. The transport fixing unitis rotatably provided as a result of being tightly stretched on the heating fixing unitand transports the medium S while contacting a surface of the medium S on which an image is formed. The pressurizing fixing unitis rotatable and is disposed to face the heating fixing unitso as to sandwich the transport fixing unittherebetween. The pressurizing fixing unitapplies pressure so as to form a fixing area FA between the pressurizing fixing unitand the heating fixing unit. The cooling unitcools the transport fixing unit. The cooling unitis disposed in a transport region of the transport fixing unitfor the medium S so as to contact the back side of the transport fixing unit. The cooling unitis located at a position farther downstream than the fixing area FA in the transport direction of the medium S. During a standby mode in which power supply to the heat sourceof the heating fixing unitis interrupted or reduced, the driving controllerexecutes drive control to cause the transport fixing unitto perform idling rotation to repeat a forward rotation operation and a reverse rotation operation so that a portion including a contact area CN where the transport fixing unitcontacts the heating fixing unitand a portion of the transport fixing unitwhich has been heated by the heating fixing unitand which has not yet reached a cooling area CA of the cooling unitcontacts the heating fixing unit.

7 1 1 7 1 1 a a In this example, a power supply unitsupplies power to the heat sourceof the heating fixing unit. The power supply unitinterrupts or reduces power supply to the heat sourceof the heating fixing unitduring the standby mode.

2 1 5 5 4 2 2 2 1 FIG.A 1 FIG.A The transport fixing unitis tightly stretched on the heating fixing unitand a separator, as illustrated in. The separatoris located farther downstream than the cooling unitin the transport direction of the medium S and is disposed at a position at which it separates the medium S from the transport fixing unit. The transport fixing unitmay be provided in a different manner from that illustrated in. For example, another member, which is not shown, may be added to tightly support the transport fixing unit.

10 11 10 The fixing deviceof the exemplary embodiment configured as described above may be built in an image forming apparatus including the image forming unitthat forms the unfixed image G. Alternatively, the fixing devicemay be built in a postprocessing device, which is different from an image forming apparatus, and may be formed as an image forming system including multiple units.

1 1 1 2 3 3 1 3 3 8 3 3 2 3 2 a The heating fixing unitincludes a heating fixing roller, for example. The heat sourcemay be built in the heating fixing unitor may be externally provided. The transport fixing unitincludes a belt-like member. The belt-like member may be constituted by an endless film made of a thermosetting polyimide resin. In order to obtain a high-gloss image, such as a photographic image, a highly smooth coating layer may be applied onto the surface of the endless film. The pressurizing fixing unitmay have a desired shape such as a roller-like shape or a belt-like shape as long as it can pressurize the medium S so as to form the fixing area FA between the pressurizing fixing unitand the heating fixing unit. If necessary, the pressurizing fixing unitmay include a heat source, which is not shown. The pressurizing fixing unitmay include a contacting/separating unitthat shifts the pressurizing fixing unitfrom a contact position to a non-contact position during the standby mode. The contact position is a position at which the pressurizing fixing unitcontacts the transport fixing unit. The non-contact position is a position at which the pressurizing fixing unitis separated from the transport fixing unit.

4 2 2 4 A wide range of devices can be used for the cooling unitif they can cool the transport fixing unitby contacting the back side of the transport fixing unitwithin a medium transport area. One of the major examples of the cooling unitis a heat dissipating unit that dissipates absorbed heat, such as a heat sink.

6 1 1 6 1 1 a a During the standby mode, in one example, the driving controllerperforms control to interrupt power supply to the heat sourceof the heating fixing unit, and, in another example, the driving controllerperforms control to reduce power supply to the heat sourceof the heating fixing unit

10 10 1 1 10 10 1 1 1 1 a a a For example, when performing warming-up between the fixing deviceof this example and another device, mutually exclusive control is executed for power supply to these devices. In this case, when warming up another device, the fixing deviceenters the standby mode and power supply to the heat sourceof the heating fixing unitis interrupted. In this manner, the fixing deviceis applicable to a case based on mutually exclusive control. However, the fixing deviceis also applicable to another type of case which does not use mutually exclusive control. During the standby mode, therefore, in one example, power supply to the heat sourceof the heating fixing unitis interrupted, and in another example, power supply to the heat sourceof the heating fixing unitis reduced.

6 2 6 The driving controllercauses the transport fixing unitto perform idling rotation during the standby mode in this example. The driving controllerexecutes this drive control in a specific manner.

2 2 1 2 2 1 2 2 1 2 1 4 2 1 2 4 2 h h c c 1 FIG.B “Idling rotation” in this example refers to that the transport fixing unitrepeatedly performs a forward rotation operation and a reverse rotation operation so that a predetermined portion of the transport fixing unitcontacts the heating fixing unit. The predetermined portion is a portion(see) of the transport fixing unitthat is heated by the heating fixing unit(which will also be called the heated portion). More specifically, the predetermined portion is a portion including a contact area CN where the transport fixing unitcontacts the heating fixing unitand an area of the transport fixing unitwhich has been heated by the heating fixing unitand has not yet reached a cooling area CA of the cooling unit. This idling rotation operation of the transport fixing unitis performed in order to suppress a temperature drop of the heating fixing unit, which is caused by a portioncooled by the cooling unit(which will also be called the cooled portion).

Typical examples and other examples of the fixing device according to an exemplary embodiment will now be described below.

1 6 6 2 1 FIG.B In one typical example, during the standby mode in which power supply to the heating fixing unitis interrupted or reduced, the driving controllerperforms the following drive control as illustrated in. The driving controllerstops the forward rotation of the transport fixing unitand causes it to start idling rotation in the reverse direction.

2 6 2 2 4 1 2 1 2 2 c c 1 FIG.C After the transport fixing unithas started idling rotation in the reverse direction, the driving controllerstops the reverse rotation of the transport fixing unitwhen the portioncooled by the cooling unithas reached a first position Pand then causes the transport fixing unitto start idling rotation in the forward direction, as illustrated in. As the first position P, any suitable position may be selected if it is a position at which the cooled portionof transport fixing unithas not yet reached the contact area CN.

2 6 2 2 1 2 2 2 2 2 4 6 2 1 2 h h 1 FIG.B After the transport fixing unithas started idling rotation in the forward direction, the driving controllerstops the forward rotation of the transport fixing unitwhen the portionheated by the heating fixing unithas reached a second position Pand causes the transport fixing unitto start idling rotation in the reverse direction, as illustrated in. As the second position P, any suitable position may be selected if it is a position at which the heated portionof the transport fixing unithas not yet reached the cooling area CA of the cooling unit. In this manner, thereafter, the driving controllercauses the transport fixing unitto repeatedly perform idling rotation in the forward direction and in the reverse direction between the first position Pand the second position P.

6 2 6 2 2 3 6 2 2 2 3 2 6 2 1 3 1 FIG.A c c In another typical example of the driving controller, after causing the transport fixing unitto start idling rotation in the forward direction, the driving controllerperforms the following drive control. As shown in, a position before the position at which the cooled portionof the transport fixing unitreaches the contact area CN is set to a third position P. In this example, the driving controllerstops the forward rotation of the transport fixing unitwhen the cooled portionof the transport fixing unithas reached the third position Pand causes the transport fixing unitto start idling rotation in the reverse direction. In this manner, thereafter, the driving controllercauses the transport fixing unitto repeatedly perform idling rotation in the forward direction and in the reverse direction between the first position Pand the third position P.

6 7 9 9 6 7 1 1 FIG.A In a typical example, the driving controllercancels the standby mode started by the power supply unitin the following manner, as illustrated in. A position detectoris disposed on the farther upstream side than the fixing area FA in the transport direction of the medium S and detects the position of the leading end or the trailing end of the medium S in the transport direction of the medium S. Based on a detection result of the position detector, the driving controllercancels the standby mode and causes the power supply unitto start supplying power to the heating fixing unit.

Typical exemplary embodiments and other exemplary embodiments of the fixing device based on the above-described exemplary embodiment will now be described below with reference to the accompanying drawings.

2 FIG. illustrates the overall configuration of an image forming system according to a first exemplary embodiment.

2 FIG. 15 16 50 16 81 81 81 16 16 a b In, an image forming systemincludes a device bodycontaining an image forming unit that can form color images. A postprocessing device, which is an optional device, is additionally provided on the top of the device body. Multiple medium supply containers(,) that supply a medium, such as sheets, are provided in the bottom side of the device bodyso as to be pulled out of the device body.

20 20 20 20 20 30 20 20 20 30 81 20 a d a d An image forming unit used in the first exemplary embodiment utilizes an electrophotographic system, for example, and includes multiple image formers. The image formersform four colors of images (yellow (Y), magenta (M), cyan (C), and black (K)), for example. In this example, the image formers(through) are arranged side by side along a belt-like intermediate transfer body, that is, they are formed in what is known as a tandem structure. For example, multiple colors of toner images formed by the individual image formers(through) are sequentially transferred onto the intermediate transfer body(this is called a first transfer operation) and are superimposed on each other. After the superimposed toner images are transferred together onto a medium S transported from the medium supply container, they are fixed on the medium S. The image formersmay not necessarily be arranged in order of Y, M, C, and K, and may be arranged in a different order.

20 20 20 21 21 22 23 24 25 26 27 22 21 23 21 22 24 21 25 21 30 25 21 30 26 21 27 21 a d The image formers(through) in the first exemplary embodiment each include a photoconductor, which serves as an image carrier that forms and carries a toner image of a corresponding color component. Around the photoconductor, a charger, an exposure device, a developing device, a first transfer device, a photoconductor cleaner, and a static eliminator, for example, are disposed. The chargeris constituted by a charging roller, for example, that charges the photoconductor. The exposure deviceis constituted by a laser scanner or a light emitting diode (LED) array, for example, that forms an electrostatic latent image on the photoconductorcharged by the charger. The developing deviceincludes a developing roller, for example, which develops an electrostatic latent image formed on the photoconductorby using a toner of a corresponding color. The first transfer deviceis disposed at a position at which it faces the photoconductorso as to sandwich the intermediate transfer bodytherebetween. The first transfer deviceis constituted by a first transfer roller or a corona discharger, for example, that performs the first transfer operation for transferring a toner image on the photoconductorto the intermediate transfer body. The photoconductor cleanerincludes a cleaning member for cleaning residual toner remaining on the photoconductor. The static eliminatoris constituted by a static eliminator roller or a corona discharger, for example, for eliminating residual electric charge remaining on the photoconductor.

23 20 20 20 a d In the first exemplary embodiment, the single exposure deviceperforms an exposure operation for the four image formers(through).

30 31 32 31 30 32 33 33 34 30 31 30 The intermediate transfer bodyis tightly stretched on multiple tension rollersand. For example, the tension rollerserves as a driving roller, which transports the intermediate transfer body. The tension rollerserves as a backup roller for a second transfer device, for example, and is located to face the second transfer device. An intermediate transfer body cleaner, which removes residual toner on the intermediate transfer body, is also disposed at a position at which it faces the tension rollerused for the intermediate transfer body.

33 33 30 32 33 33 32 30 a a In this example, the second transfer deviceincludes a second transfer rollerthat contacts the front side of the intermediate transfer bodywhich faces the tension roller. In this example, the second transfer deviceapplies a second transfer electric field to between the second transfer rollerand the tension rollerso as to transfer images on the intermediate transfer bodytogether onto the medium S (this is called a second transfer operation).

16 35 30 24 20 35 24 Inside the device body, toner boxesare provided above the intermediate transfer bodyso as to correspond to the developing devicesof the individual image formers. The individual toner boxessupply toner to the developing devicesof the corresponding colors via a transport path, which is not shown.

80 81 82 83 84 85 40 85 81 33 40 33 86 40 86 50 87 87 16 A medium transport systemin the first exemplary embodiment is formed as follows. A medium is fed from each medium supply containerby a pickup roller. Then, the medium is sorted by a feed rollerand a retard rollerand only one sheet of medium is transported to the transport path on the downstream side. In the transport path, matching rollersand a first fixing unitare provided. The matching rollersdetermine the position of the medium S carried from the medium supply containerbefore the medium S enters the second transfer device. The first fixing unitfixes an unfixed toner image transferred onto the medium S by the second transfer device. A switching member, which switches the transport path, is provided on the downstream side of the first fixing unit. In this example, the switching memberswitches the transport path between two directions, which are toward the postprocessing deviceand toward a first output receiver. The first output receiverstores a medium directly output from the device body.

81 81 81 81 81 a b As the medium supply container, two medium supply containersandthat store different sizes of sheets of medium are shown by way of example. However, this is only an example, and three or more medium supply containersmay be provided, or only one medium supply containermay be provided. A manual feeder, which is not shown, may be provided, and a medium may be fed from the manual feeder to the transport path.

40 41 42 41 42 41 42 41 40 The first fixing unitin the first exemplary embodiment includes a heating fixing rollerand a pressurizing fixing roller, for example. The heating fixing rollerhas a built-in heat source, such as a halogen lamp, which is not shown. The pressurizing fixing rolleris disposed to face the heating fixing rollerand transports a medium by sandwiching it to a fixing area formed between the pressurizing fixing rollerand the heating fixing roller. With this configuration, when a medium having an unfixed toner image held thereon passes through the fixing area of the first fixing unit, the unfixed toner image is fixed onto the medium by the application of heat and pressure.

40 40 In this example, a pair of a heating roller and a pressurizing roller is used for the first fixing unit. However, the first fixing unitis not limited to this configuration, and suitable members can be selected. For example, a medium may be held in a fixing area formed between a heating fixing roller and a pressurizing fixing belt, and an unfixed image on the medium may be fixed by the application of heat and pressure. In this case, a pressurizing pad is provided to face the heating fixing roller, and the pressurizing fixing belt is interposed between the heating fixing roller and the pressurizing pad. In this example, the pressurizing fixing belt is rotated by the rotation of the heating fixing roller.

2 FIG. 50 60 70 60 51 70 60 88 50 70 As illustrated in, the postprocessing deviceincludes a second fixing unitand a cutting device. The second fixing unitis provided in a mid-portion of a medium transport pathand processes a toner image surface of a medium into a high-gloss surface. The cutting devicecuts a medium having passed through the second fixing unit. In the first exemplary embodiment, a second output receiveris provided on the downstream side of the postprocessing deviceand stores a medium having passed through the cutting device.

60 70 Before giving a detailed explanation of the second fixing unit, the cutting devicewill first be explained below.

70 70 71 72 72 72 71 72 70 73 74 2 FIG. a b In the first exemplary embodiment, the cutting devicecan cut sides of a medium and form a borderless print sheet, for example. To implement this purpose, as shown in, the cutting deviceincludes a slitterand circular cutters(,). The slitteris a member which cuts a medium along the width, while the circular cutteris a member which cuts the medium along the length in the feeding direction. The cutting devicealso includes multiple transport rollersandto transport a medium.

71 72 72 In this example, the slitterhas a required number of blades in the axial direction in accordance with the number of pieces to be produced by cutting a medium and cuts the medium in the feeding direction while transporting it. The circular cuttertemporarily stops the transportation of a medium and then cuts the medium by moving a rolling cutter having an upper blade along a lower blade. As the circular cutter, a roller cutter may be provided in the axial direction and cut a medium while transporting it.

70 70 70 70 71 The cutting devicehas, not only a function of cutting a medium into multiple (four, for example) pieces, but also other functions. As an example of the other functions of the cutting device, one L-size (standard photo size in Japan, which is equivalent to 3R size (standard photo size in the United States)) image is printed on a postcard-size medium (100×150 mm), and the cutting devicecan finish the medium as a borderless print sheet. As another example of the other functions of the cutting device, a desired number of L-size (3R-size) images, such as photographic images using a digital camera, can be obtained. For example, four images are printed on an A4-size medium, and then, the four images are printed one by one on a desired number of postcard-size mediums. Additionally, as a result of varying the widthwise position of the blades of the slitter, a medium can be cut into various sizes, such as into four pieces, six pieces, and eight pieces.

60 10 1 FIG.A The basic configuration of the second fixing unitis similar to that of the fixing deviceshown in.

2 3 FIGS.andA 60 61 62 63 64 That is, as illustrated in, the second fixing unitincludes a heating fixing roller, a transport fixing belt, a pressurizing fixing roller, and a cooling unit.

61 65 62 61 62 63 61 62 63 61 1 FIG.A 1 FIG.A 1 FIG.A The heating fixing roller, which corresponds to the above-described heating fixing unit (see), includes a built-in heat sourcein this example. The transport fixing belt, which corresponds to the above-described transport fixing unit (see), is rotatably provided as a result of being tightly stretched on the heating fixing roller. The transport fixing belttransports the medium S while contacting the surface of the medium S on which an image is formed. The pressurizing fixing roller, which corresponds to the above-described pressurizing fixing unit (see), is disposed to face the heating fixing rollerso as to sandwich the transport fixing belttherebetween. The pressurizing fixing rolleris pressed against the heating fixing rollerso as to form a fixing area FA therebetween.

64 62 62 64 62 1 FIG.A The cooling unit, which corresponds to the above-described cooling unit (see), is disposed in a space surrounded by the transport fixing beltand cools the transport fixing belt. In this example, the cooling unitis located farther downstream than the fixing area FA in the transport direction of the medium S and is disposed to contact the back side of the transport fixing beltwithin a medium transport area SA.

61 61 65 61 65 61 61 69 62 a a 5 FIG. The heating fixing rolleris formed by applying a release layer (not shown) constituted by a PFA tube, for example, onto the surface of a metal corehaving high heat conductivity. A heat source, such as a halogen lamp, is provided inside the core. Heating of the heat sourceis controlled so that the surface of the heating fixing rollerhas a predetermined temperature. The heating fixing rolleris driven to rotate by a drive motor(see) so as to rotate the transport fixing belt.

3 FIG.B 62 62 62 62 62 62 a b a b As illustrated in, the transport fixing beltis constituted by an endless film base membermade of a thermosetting polyimide resin, for example, coated with a highly smooth coating layermade of fluorine rubber or silicone rubber, for example. As the film base memberand the coating layerof the transport fixing belt, a base member and a coating layer each having a suitable thickness are selected to maintain the mechanical strength and to efficiently utilize thermal energy. For example, a base member having a thickness of about 75 μm coated with a coating layer having a thickness of about 35 μm is used.

62 61 67 61 The transport fixing beltis tightly stretched on the heating fixing rollerand a separating rollerso as to be rotated by the rotation of the heating fixing roller.

67 62 67 62 67 62 62 67 62 62 1 FIG.A The separating rollercorresponds to the above-described separator (see) and separates the medium S from the transport fixing belt. The separating rolleris rotated by following the movement of the transport fixing belt. The separating rollertightly supports the transport fixing beltthereon while winding it up so as to cause a sudden change in the moving direction of the transport fixing belt. Because of this configuration, at the position of the separating roller, the medium S on the transport fixing beltis separated from the transport fixing beltby itself because of the stiffness of the medium S.

62 61 67 62 62 67 61 62 62 62 62 62 The transport fixing beltis tightly stretched on the heating fixing rollerand the separating rollerin this example. However, the transport fixing beltmay be provided in a different manner. For example, a steering roller, which is not shown, may be provided in a region where the transport fixing beltreturns from the separating rollerto the heating fixing roller. In this case, the steering roller presses the transport fixing beltoutwardly to maintain the tension of the transport fixing belt. The steering roller tilts the rotating axis of oneself to correct the position of the transport fixing beltwhich is displaced to one side while rotating. The displacement of the transport fixing beltto one side refers to that the transport fixing beltis shifted toward one of the two ends in a direction of the rotating axis of the steering roller.

63 63 63 61 63 66 63 63 66 63 60 61 63 62 b a b a The pressurizing fixing rolleris formed such that an elastic layermade of silicone rubber, for example, covers the surface of a metal corehaving high heat conductivity. A release layer (not shown) similar to that of the heating fixing rolleris formed on the surface of the elastic layer. In the first exemplary embodiment, a heat source, such as a halogen lamp, is provided inside the coreof the pressurizing fixing roller. Heating of the heat sourceis controlled so that the surface of the pressurizing fixing rollerhas a predetermined temperature. The medium S transported to the second fixing unitpasses through the fixing area FA formed between the heating fixing rollerand the pressurizing fixing roller. At this time, a toner image on the medium S is heated and pressurized in a state in which the toner image surface of the medium S contacts the transport fixing belt.

63 66 66 63 In this example, the pressurizing fixing rollerincludes the heat source. However, the provision of the heat sourcein the pressurizing fixing rollermay be omitted.

64 61 67 62 64 62 64 62 62 62 In the first exemplary embodiment, the cooling unitis provided in a region between the heating fixing rollerand the separating roller(this region corresponds to the medium transport area SA) in a state in which it contacts the back side of the transport fixing belt. The cooling unitcontacts a portion of the medium transport area SA of the transport fixing beltand uses this contact portion as the cooling area CA. In the cooling area CA, the cooling unitcools the transport fixing beltby absorbing heat of the transport fixing belt. With this configuration, the medium S, which is transported while closely contacting the transport fixing belt, can be cooled.

64 64 64 64 62 64 64 64 64 a b a b a a The cooling unitin the first exemplary embodiment corresponds to a heat sink and includes a fin memberand a cover member. The fin memberincludes many heat dissipating fins extending substantially perpendicular to the surface of the transport fixing belt. The cover memberis formed in a tubular shape having a rectangular cross section so as to cover the fin member. The cooling unituses an air blower, which is not shown, to cause air to flow inside, thereby dissipating heat in the fin memberto the outside.

641 64 64 641 5 FIG. a A temperature sensor(see) is disposed on part of the fin member, for example. The cooling unitturns the air blower ON or OFF or controls the air volume of the air blower, based on a detection result of the temperature sensor.

64 64 64 62 3 FIG.A In the first exemplary embodiment, in terms of securing the cooling effect of the cooling unit, the cooling unitis formed as shown in. That is, in this example, the medium S can be located to closely contact the cooling area CA of the cooling unitwhile being transported by the transport fixing belt.

111 62 64 111 62 62 In this example, an inlet opposing rolleris provided on the front side of the transport fixing beltat a portion corresponding to the inlet (upstream start point A) of the cooling area CA of the cooling unit. The inlet opposing rolleris disposed to contact the transport fixing beltand is rotated by following the movement of the transport fixing belt.

112 62 64 112 62 62 An outlet opposing rolleris provided on the front side of the transport fixing beltat a portion corresponding to the outlet (downstream end point B) of the cooling area CA of the cooling unit. The outlet opposing rolleris disposed to contact the transport fixing beltand is rotated by following the movement of the transport fixing belt.

111 112 In this manner, each of the inlet opposing rollerand the outlet opposing rollerserves as an opposing rotator.

111 111 62 62 In this example, the inlet opposing rolleris located at a portion corresponding to the inlet of the cooling area CA. By positioning the inlet opposing rollerat this portion, the medium S transported by the transport fixing beltis pulled in at the inlet of the cooling area CA so as to closely contact the transport fixing belt.

112 62 112 62 111 112 112 The provision of the outlet opposing rolleris effective in closely contacting the medium S to the transport fixing belt. More specifically, the outlet opposing rollerserves to closely contact the medium S to the transport fixing belt, together with the inlet opposing roller, at two leading and trailing locations in the transport direction of the medium S. The outlet opposing rolleris disposed at a portion corresponding to the outlet of the cooling area CA. However, the position of the outlet opposing rolleris not limited to this portion and may be provided farther upstream than the outlet of the cooling area CA.

4 FIG.A 2 1 3 2 Typically, to obtain a high-gloss image, such as a photographic image, a special sheet, such as that shown in, may be used as the medium S. In this special sheet, a moisture-proof layer Lis applied onto each side of a base member layer L, and an image receiving layer Lis provided on a recording surface (surface on which a toner image is to be formed) of the moisture-proof layer L. This structure is similar to that of photographic paper used for a silver halide print, for example.

2 1 3 1 1 The moisture-proof layer Lis made of a resin having no permeability, such as polyethylene, and has a thickness of about several micrometers to exhibit a moisture-proof effect for the base member layer L. The image receiving layer Lis made of a thermosetting resin, as a principal component, such as polyester, having a melting temperature of about 130° C. and has a thickness of 5 to 20 μm, and more preferably, about 10 sm. The base member layer Lhas a composition similar to that of plain paper, which is made of cellulose as a principal component. Alternatively, a special base member layer Lhaving a composition different from that of plain paper may be used.

2 1 3 2 1 1 (1) The medium S does not have permeability and thus prevents some inconveniences, which may be caused if the base member layer Labsorbs moisture under a high humidity environment. Examples of the inconveniences are the occurrence of curling due to the extension of the base member layer Land the occurrence of cracking due to the extension of a toner image. 3 3 3 (2) A toner image can be embedded into the image receiving layer Lin a good state, thereby obtaining a smooth surface of the printed medium S. This is because a toner image can melt together with the image receiving layer Land be embedded into the image receiving layer Lwith the application of pressure. As the medium S, therefore, a medium having a moisture-proof layer Lon each side of a base member layer Land having an image receiving layer Lmade of a material similar to a toner material on the recording surface of the moisture-proof layer Lmay be selected. Using such a medium S obtains the following effects.

60 3 62 60 3 40 1 1 4 FIG.B 4 FIG.C In a photograph print mode, if the second fixing unitperforms a fixing operation using such a special sheet, the resulting toner image is embedded into the image receiving layer L, as shown in. At this time, the surface texture of the transport fixing beltof the second fixing unitis reflected, which makes the surface of the image receiving layer Land the surface of the toner image substantially uniform, resulting in a high-gloss image. In contrast, in a plain paper print mode, a toner image is fixed on plain paper used as the medium S only with the first fixing unit. In this case, as shown in, the toner image is merely mounted on the base member layer Land is projected from the surface of the base member layer L, resulting in an image having poor gloss characteristics.

5 FIG. 60 52 60 53 51 In this example, as illustrated in, near the entrance of the second fixing unit, an entrance guiding memberis provided to guide the medium S into the entrance of the second fixing unit. A position sensoris also provided to detect the position of the leading end or the trailing end of the medium S which is to pass through the transport path.

60 54 60 55 54 Near the exit of the second fixing unit, an exit guiding memberis provided to guide the medium S output from the exit of the second fixing unit. Transport rollersare provided on the downstream side of the exit guiding member.

60 56 60 56 In this example, to obtain a high-gloss image, the separation temperature Ts of the medium S at the separation position of the second fixing unitis adjusted to be a predetermined threshold temperature or lower. To adjust the temperature Ts of the medium S, a contactless temperature sensoris disposed near the separation position of the second fixing unitand measures the temperature Ts of the medium S at the separation position. As the temperature sensor, a radiation thermometer is used.

5 FIG. 60 150 In this example, as illustrated in, the control system of the second fixing unitincludes a control deviceconstituted by a microcomputer including various processors. The term “processor” refers to hardware in a broad sense. Examples of the processor include general processors (e.g., CPU: Central Processing Unit) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, and programmable logic device).

151 15 150 151 150 An operation panelof the image forming systemis connected to the control device. In the operation panel, a start switch (SW) for causing the control deviceto start processing for forming an image on the medium S, a mode switch (SW) for selecting an image forming mode, such as single-sided printing, double-sided printing, or high-definition printing, and a medium type specifier for specifying a medium type to be used, for example, are provided.

150 60 60 60 In a read only memory (ROM), which serves as a storage of the control device, programs for controlling the second fixing unitare preinstalled. These programs include a program for executing power supply processing for controlling power supply to the second fixing unitand a program for executing processing for individual operation modes of the second fixing unit. The processing for individual operation modes includes fixing processing for the regular operation mode and waiting processing for the standby mode.

60 60 In this example, in the power supply processing, the amount of heating power to be supplied to the second fixing unitis controlled in accordance with the operation mode of the second fixing unit. In this example, the normal amount of heating power is supplied in the regular operation mode, while the supply of heating power is interrupted or the supply amount of heating power is reduced during the standby mode.

62 64 The fixing processing for the regular operation mode includes heating and pressurizing processing performed in the fixing area FA for the medium S transported by the transport fixing beltand cooling processing performed by the cooling unit.

62 60 62 62 The waiting processing for the standby mode is processing for causing the transport fixing beltto wait when the supply of heating power to the second fixing unitis interrupted or reduced. In this example, as the waiting processing, the transport fixing beltis driven to perform idling rotation so as to suppress a temperature drop of a heated portion of the transport fixing beltduring the standby mode.

53 56 641 150 69 65 66 150 Various detectors, such as the position sensorand the temperature sensorsand, are connected to the control device. Various control targets, such as the drive motorand the heat sourcesand, are also connected to the control device.

150 151 The processor of the control devicereceives an instruction signal from the operation paneland detection signals from various detectors, executes the above-described programs, and sends suitable control signals to the control targets.

15 The basic operation of the image forming systemwill now be described below.

2 FIG. 20 20 20 30 30 81 33 a d As shown in, the individual colors of toner images formed by the image formers(through) are transferred onto the intermediate transfer bodyin the first transfer operation and are transported to a second transfer region. The superimposed toner images held on the intermediate transfer bodyare transferred together onto the medium S fed from the medium supply containerby the second transfer devicein the second transfer operation.

40 87 88 50 86 The unfixed toner images transferred onto the medium S together are fixed by the first fixing unit. Then, the medium S having the fixed toner image thereon is guided to the first output receiveror to the second output receivervia the postprocessing deviceby the switching member.

86 86 In the first exemplary embodiment, the switching memberswitches the medium transport direction in the following manner. The switching memberswitches the medium transport direction in accordance with whether the plain paper print mode or the photograph print mode is used. The plain paper print mode is a mode in which a regular image, that is, a low-gloss print sheet, is formed. The photograph print mode is a mode in which a high-gloss image, such as a photographic image, that is, a high-gloss print sheet, is formed.

40 87 86 40 60 86 60 88 70 70 88 70 In the plain paper print mode, the medium S subjected to the fixing operation by the first fixing unitis output to the first output receiverby the switching member. In the photograph print mode, the medium S subjected to the fixing operation by the first fixing unitis output to the second fixing unitby the switching member. Then, the medium S is subjected to the fixing operation by the second fixing unitand is output to the second output receivervia the cutting device. The cutting devicecan be used when a borderless print sheet, such as a photographic image, is to be output, for example. If it is not necessary to cut the medium S, the medium S is simply output to the second output receiverwithout using the cutting device.

4 FIG.A Typically, to obtain a high-gloss image, such as a photographic image, a special sheet, such as that shown in, may be used as the medium S.

60 3 62 60 3 4 FIG.B In the photograph print mode, when the second fixing unitperforms a fixing operation using such a special sheet, the resulting toner image is embedded into the image receiving layer L, as shown in. At this time, the surface texture of the transport fixing beltof the second fixing unitis reflected, which makes the surface of the image receiving layer Land the surface of the toner image substantially uniform, resulting in a high-gloss image.

60 In the regular operation mode, the fixing operation of the second fixing unitis performed as follows.

50 40 60 60 61 63 65 66 62 61 3 FIG.A The medium S guided to the postprocessing devicevia the first fixing unitis about to enter the second fixing unit, as shown in. In this state, in the second fixing unit, the heating fixing rollerand the pressurizing fixing rollerare respectively heated by the heat sourcesandto the temperatures at which they can fix a toner image onto the medium S. The transport fixing beltis rotating in accordance with the rotation of the heating fixing roller.

64 The cooling unitis in the standby state to perform a cooling operation by driving the air blower.

62 64 60 In this state, the medium S is heated and pressurized in the fixing area FA and is then transported by the transport fixing belt. Then, the heated medium S is cooled by the cooling unitand is then separated at the separation position of the second fixing unit.

60 4 FIG.A In this manner, the medium S undergoes a series of fixing processing, that is, heating and pressurizing processing and then cooling processing, in the second fixing unit. As a result, with the use of a special sheet, such as that shown in, a high-gloss image, such as a photographic image, can be obtained.

15 40 60 40 60 40 60 40 60 15 40 60 40 60 40 60 40 60 40 60 40 60 60 40 40 60 60 In the first exemplary embodiment, the image forming systemincludes two fixing units, that is, the first fixing unitand the second fixing unit. Since the first fixing unitand the second fixing uniteach include a heat source, a sufficient amount of heating power is required for starting (warming-up) the first fixing unitand the second fixing unit. In such a situation, the upper limit of allowable power that can be used by the first fixing unitand the second fixing unitat the same time is usually determined for the image forming system. To start the first fixing unitand the second fixing unittogether, heating power is supplied to each of the first fixing unitand the second fixing unitat the same time. In this case, a sufficiently large amount of power is supplied to the first fixing unitand the second fixing unit, which may exceed the upper limit of allowable power. To avoid such a situation, mutually exclusive control may be performed for the supply of heating power to the first fixing unitand the second fixing unit. Mutually exclusive control is a control method such that, when heating power is supplied to one of the first fixing unitand the second fixing unit, the supply of heating power to the other one of the first fixing unitand the second fixing unitis interrupted. For example, the second fixing unit, which takes more time for warming-up, is first started, and the first fixing unit, which takes less time for warming-up, is started later. While the first fixing unitis being started, the supply of heating power to the second fixing unitis interrupted and the second fixing unitenters the standby mode to prepare for the regular operation.

40 60 In this example, when the supply of heating power to one of the first fixing unitand the second fixing unitis not interrupted but is reduced, too, this fixing unit is shifted to the standby mode.

60 15 40 60 62 60 60 60 The supply of heating power to the second fixing unitis reduced in the following case, for example. When the image forming systemis in the plain paper print mode, for example, only the first fixing unitis used. If the second fixing unitis driven as in the regular operation mode, the transport fixing beltis rotated wastefully and is repeatedly heated and cooled, thereby wasting power. In this example, therefore, the supply of heating power to the second fixing unitis reduced, and the second fixing unitenters the standby mode. With a reduced amount of heating power supplied to the second fixing unitduring the standby mode, power is consumed less than that in the regular operation mode.

62 62 62 64 62 61 61 60 Typically, during the standby mode, the transport fixing beltis driven to perform idling rotation in a predetermined direction. With this method, however, when the supply of heating power is interrupted or reduced, the temperature of the transport fixing beltis lowered. More specifically, the transport fixing beltis cooled by the cooling unit, and the cooled transport fixing beltcontacts the heating fixing rollerand lowers the temperature of the heating fixing unit, too. When the operation mode is returned from the standby mode to the regular operation mode, a larger amount of heating power is required for the second fixing unit.

60 6 FIG. Drive control processing for the second fixing unitduring the standby mode will be described below with reference to the flowchart of.

6 FIG. 60 60 60 In, it is first determined whether the supply of heating power to the second fixing unitis to be interrupted or reduced. If the supply of heating power to the second fixing unitis not to be interrupted or reduced, the second fixing unitmaintains the regular operation mode.

60 60 If the supply of heating power to the second fixing unitis to be interrupted or reduced, the second fixing unitshifts to the standby mode.

150 65 61 66 63 Then, in this example, the control deviceinterrupts or reduces power supply to the heat sourceof the heating fixing rollerand the heat sourceof the pressurizing fixing roller.

150 62 7 FIG.A The control devicealso stops driving the transport fixing beltand causes it to start idling rotation in the reverse direction, as shown in.

61 62 62 62 64 62 c h. In this state, the heating fixing rolleris driven to rotate in the reverse direction and the transport fixing beltis rotated and moved in the reverse direction. At this time, the transport fixing beltincludes a cooled portioncooled by the cooling unit, as well as a heated portion

62 62 61 62 61 64 62 62 62 62 62 64 h c h c The heated portionincludes the contact area CN where the transport fixing beltcontacts the heating fixing rollerand the area of the transport fixing beltwhich has been heated by the heating fixing rollerand which has not yet reached the cooling unit. The cooled portionis a portion of the transport fixing beltother than the heated portion. More specifically, the cooled portionis constituted by a portion of the transport fixing beltwhich is passing through the cooling area CA of the cooling unitand a portion which has passed through the cooling area CA.

7 7 FIGS.A throughD 62 62 62 h c In, the heated portionof the transport fixing beltis indicated by a cross hatch pattern, while the cooled portionis left blank.

150 62 62 1 62 150 1 64 1 1 150 61 62 c c 7 FIG.B 7 FIG.A Then, the control devicestops the transport fixing beltwhen the cooled portionhas reached the first position P, as illustrated in. As the first position, a position right before the position at which the cooled portionreaches the contact area CN (see) is selected. The control devicehas stored distance information Jof the distance from the inlet of the cooling area CA of the cooling unitto the first position P. Based on the distance information J, the control devicedrives the heating fixing rollerto rotate in the reverse direction and then stops the rotation so as to move the transport fixing beltby a predetermined distance.

62 62 1 61 63 62 c c. In this state, the cooled portionof the transport fixing beltremains at the first position Pand does not reach the contact area CN. It is thus unlikely that the temperature of the heating fixing rollerand that of the pressurizing fixing rollerare lowered by the cooled portion

62 62 62 62 62 h h In accordance with the rotation and the movement of the transport fixing beltin the reverse direction, the heated portionis moved to reach the lower belt portion of the transport fixing belt. When the transport fixing belthas stopped moving, the heated portionextends to the outside of the contact area CN.

150 62 61 62 7 FIG.B Then, the control devicedrives the transport fixing beltto perform idling rotation in the forward direction, as shown in. The heating fixing rolleris driven to rotate in the forward direction, which rotates and moves the transport fixing beltin the forward direction.

150 62 62 2 62 150 2 1 2 2 150 61 62 h h Then, the control devicestops the transport fixing beltwhen the heated portionhas reached the second position P. As the second position, a position right before the position at which the heated portionreaches the cooling area CA is selected. The control devicehas stored distance information Jof the distance from the first position Pto the second position P. Based on the distance information J, the control devicedrives the heating fixing rollerto rotate in the forward direction and then stops the rotation so as to move the transport fixing beltby a predetermined distance.

62 62 2 62 64 h h In this state, the heated portionof the transport fixing beltremains at the second position Pand does not reach the cooling area CA. It is thus unlikely that the temperature of the heated portionis lowered by the cooling unit.

62 62 62 62 62 62 62 62 2 1 2 62 1 1 1 2 2 62 62 61 62 62 h c h c h h c c In accordance with the rotation and the movement of the transport fixing beltin the forward direction, the heated portion, which extends to the outside of the contact area CN in the lower belt portion of the transport fixing belt, is moved in the forward direction. The lower belt portion of the transport fixing beltincludes the cooled portionnext to the heated portionextending to the outside of the contact area CN. In this example, however, this cooled portiondoes not reach the contact area CN. This will be explained below in detail. The amount by which the transport fixing beltis shifted in the forward direction is based on the distance information Jof the distance between the first position Pand the second position P. In contrast, the length of the heated portionextending to the outside of the contact area CN is based on the distance information Jof the distance between the inlet of the cooling area CA and the first position P. The distance indicated by the distance information Jis longer than that of the distance information Jby the length between the inlet of the cooling area CA and the second position P. Hence, when the heated portionextending to the outside of the contact area CN is moved in the forward direction, the cooled portiondoes not reach the contact area CN. It is thus unlikely that the temperature of the heating fixing rolleris lowered by the cooled portionof the transport fixing belt.

150 62 62 2 150 61 2 62 62 1 h c 7 FIG.C Then, the control devicedrives the transport fixing belt, whose heated portionis stopped at the second position P, to perform idling rotation in the reverse direction, as shown in. At this time, the control devicedrives the heating fixing rollerto rotate in the reverse direction and then stops the rotation, based on the distance information J. Then, the transport fixing beltis rotated in the reverse direction and is stopped when the cooled portionhas reached the first position P.

7 FIG.D 150 62 1 2 62 In this manner, thereafter, as illustrated in, the control devicedrives the transport fixing beltto repeatedly perform idling rotation in the forward direction and in the reverse direction, by using the first position Pand the second position Pas the reference positions to stop the transport fixing belt.

62 62 62 61 62 64 62 61 63 62 h h h In this manner, idling rotation of the transport fixing beltin the forward direction and in the reverse direction is performed so that the heated portionof the transport fixing beltcontacts the heating fixing roller. The heated portiondoes not reach the cooling area CA of the cooling unitand the temperature of the heated portionis not unnecessarily lowered. Hence, the temperature of the heating fixing rollerand that of the pressurizing fixing rollerare not lowered by the idling rotation of the transport fixing belt.

62 62 62 61 62 61 c c To put it another way, idling rotation of the transport fixing beltin the forward direction and in the reverse direction is performed so that the cooled portionof the transport fixing beltdoes not reach the contact area CN. The heating fixing rolleris thus prevented from being cooled by the cooled portion. The temperature of the heating fixing rolleris not unnecessarily lowered.

62 Idling rotation of the transport fixing beltin the forward direction and in the reverse direction is repeatedly performed until the standby mode is canceled.

60 40 (1) when the first fixing unithas shifted to the standby mode; and 60 (2) when a medium S to be fixed by the second fixing unithas been transported and passed through a predetermined position. In this example, examples of the case where the standby mode of the second fixing unitis canceled as follows:

150 60 When the standby mode is canceled, the control devicereturns the second fixing unitto the regular operation mode.

62 1 2 62 In the first exemplary embodiment, during the standby mode, the transport fixing beltperforms forward and reverse idling rotation by using the first position Pand the second position Pas the reference positions to stop the transport fixing belt.

62 However, idling rotation of the transport fixing beltduring the standby mode is not limited to this configuration and may be modified as in the following modified example.

8 FIG. 60 is a flowchart illustrating drive control processing for the second fixing unitaccording to a modified example of the first exemplary embodiment.

8 FIG. 60 60 In, if the supply of heating power to the second fixing unitis not to be interrupted or reduced, the second fixing unitmaintains the regular operation mode.

60 60 If the supply of heating power to the second fixing unitis to be interrupted or reduced, the second fixing unitshifts to the standby mode.

60 150 65 61 66 63 (1) Power supply to the heat sourceof the heating fixing rollerand the heat sourceof the pressurizing fixing rolleris interrupted or reduced. 62 62 9 FIG.A (2) Driving of the transport fixing beltis stopped and the transport fixing beltis driven to start idling rotation in the reverse direction (see). 62 62 1 62 62 1 1 62 62 62 c c h 9 FIG.B (3) The rotation of the transport fixing beltis stopped when the cooled portionhas reached the first position P(see). At this time, in the upper belt portion of the transport fixing belt, the cooled portionremains at the first position Pand does not reach the contact area CN beyond the first position P. In the lower belt portion of the transport fixing belt, when the transport fixing belthas stopped moving, the heated portionextends to the outside of the contact area CN. 62 9 FIG.B (4) The transport fixing beltis driven to start idling rotation in the forward direction (see). After the second fixing unithas shifted to the standby mode, the control devicefirst executes the following processing operations (1) through (4) in a manner similar to the first exemplary embodiment.

9 9 FIGS.A throughD 62 62 62 h c In, the heated portionof the transport fixing beltis indicated by a cross hatch pattern, while the cooled portionis left blank.

150 62 62 3 62 3 62 64 150 3 62 3 62 1 3 1 3 3 1 3 c c h h Then, unlike the first exemplary embodiment, the control devicestops the transport fixing beltwhen the cooled portionhas reached a third position Pin the lower belt portion of the transport fixing belt. As the third position P, a position before the position at which the cooled portioncooled by the cooling unitreaches the contact area CN is selected. The control devicehas stored distance information Jof the distance from the forward end of the heated portionextending to the outside of the contact area CN to the third position P. The distance from the forward end of the heated portionextending to the outside of the contact area CN to the contact area CN corresponds to the distance indicated by the distance information J. The distance information Jis calculated from the distance information Jand the position information of the third position P. In this example, the distance indicated by the distance information Jis shorter than that of the distance information Jby the length between the third position Pand the contact area CN.

3 150 61 62 Based on the distance information J, the control devicedrives the heating fixing rollerto rotate in the forward direction and then stops the rotation so as to move the transport fixing beltby a predetermined distance.

62 62 3 3 61 62 c c. In this state, in the lower belt portion of the transport fixing belt, the cooled portionremains at the third position Pand does not reach the contact area CN beyond the third position P. It is thus unlikely that the temperature of the heating fixing rolleris lowered by the cooled portion

62 62 62 3 1 62 64 62 62 h h h When the transport fixing beltis rotated and moved in the forward direction, the heated portionin the upper belt portion of the transport fixing beltis shifted in the forward direction. In this example, since the distance indicated by the distance information Jis shorter than that of the distance information J, the heated portiondoes not reach the cooling area CA of the cooling unit. It is thus unlikely that the temperature of the heated portionof the transport fixing beltis lowered by the cooling area CA.

150 62 62 3 150 61 3 62 62 1 c c 9 FIG.C Then, the control devicedrives the transport fixing belt, whose cooled portionremains at the third position P, to perform idling rotation in the reverse direction, as shown in. At this time, the control devicedrives the heating fixing rollerto rotate in the reverse direction and then stops the rotation, based on the distance information J. Then, the transport fixing beltis rotated in the reverse direction and is stopped when the cooled portionhas reached the first position P.

9 FIG.D 150 62 1 3 62 In this manner, thereafter, as illustrated in, the control devicedrives the transport fixing beltto repeatedly perform forward and reverse idling rotation by using the first position Pand the third position Pas the reference positions to stop the transport fixing belt.

62 62 62 62 64 62 h h h In this example, forward and reverse idling rotation of the transport fixing beltis performed so that the heated portionof the transport fixing beltdoes not contact the cooling area CA. Accordingly, the heated portiondoes not reach the cooling area CA of the cooling unitand the temperature of the heated portionis not unnecessarily lowered.

62 62 62 61 62 61 c c To put it another way, forward and reverse idling rotation of the transport fixing beltis performed so that the cooled portionof the transport fixing beltdoes not touch the contact area CN. The heating fixing rolleris thus prevented from being cooled by the cooled portion. The temperature of the heating fixing rolleris not unnecessarily lowered.

62 Forward and reverse idling rotation of the transport fixing beltis repeatedly performed until the standby mode is canceled, as in the first exemplary embodiment.

150 60 When the standby mode is canceled, the control devicereturns the second fixing unitto the regular operation mode, as in the first exemplary embodiment.

10 FIG. 60 illustrates the major part of a second fixing unitaccording to a second exemplary embodiment.

10 FIG. 60 63 In, the basic configuration of the second fixing unitaccording to the second exemplary embodiment is similar to that of the first exemplary embodiment. In the second exemplary embodiment, however, control processing executed during the standby mode is partially different from that of the first exemplary embodiment because of a difference in the configuration of the pressurizing fixing roller. Elements similar to those of the first exemplary embodiment are designated by like reference numerals and a detailed explanation thereof will be omitted.

60 61 62 63 64 In this example, the second fixing unitincludes a heating fixing roller, a transport fixing belt, a pressurizing fixing roller, and a cooling unit.

63 66 63 63 130 63 130 63 63 62 63 62 130 63 63 a Unlike the first exemplary embodiment, the pressurizing fixing rollerdoes not include a heat sourcewithin a core. The pressurizing fixing rollerincludes a contacting/separating mechanism, which serves as a contacting/separating unit that selectively contacts or separates the pressurizing fixing roller. The contacting/separating mechanismshifts the pressurizing fixing rollerbetween a contact position and a non-contact position. The contact position is a position at which the pressurizing fixing rollercontacts the transport fixing beltin the fixing area FA. The non-contact position is a position at which the pressurizing fixing rolleris separated from the transport fixing belt. In this example, any suitable member may be used as the contacting/separating mechanismif it can shift the pressurizing fixing rollerto the contact position and to the non-contact position. For example, a bearing member of the pressurizing fixing rolleris supported by a movable support member, and the position of the movable support member is changed by an eccentric cam member that is rotated by a drive motor.

150 60 5 FIG. 11 FIG. In this example, the control device(see) executes drive control processing for the second fixing unitaccording to the flowchart of.

60 60 If the supply of heating power to the second fixing unitis not to be interrupted or reduced, the second fixing unitmaintains the regular operation mode.

60 60 If the supply of heating power to the second fixing unitis to be interrupted or reduced, the second fixing unitshifts to the standby mode.

60 150 After the second fixing unithas shifted to the standby mode, the control deviceexecutes the following processing operations (1) through (7).

12 12 FIGS.A throughD 12 12 FIGS.A throughD 60 62 62 62 h c 65 61 (1) Power supply to the heat sourceof the heating fixing rolleris interrupted or reduced. 62 63 62 12 FIG.A (2) Driving of the transport fixing beltis stopped and the pressurizing fixing rolleris separated from the transport fixing beltand is shifted to the non-contact position (see). 62 62 1 12 FIG.B 12 FIG.C c (3) Then, the transport fixing beltis driven to perform idling rotation in the reverse direction (see) and is stopped when the cooled portionhas reached the first position P(see). schematically illustrate idling rotation of the second fixing unitduring the standby mode. In, the heated portionof the transport fixing beltis indicated by a cross hatch pattern, while the cooled portionis left blank.

62 62 1 1 62 61 63 63 62 62 63 c h h h At this time, in the upper belt portion of the transport fixing belt, the cooled portionremains at the first position Pand does not reach the contact area CN beyond the first position P. The heated portionis passing through the contact area CN while contacting the heating fixing rollerbut separating from the pressurizing fixing roller. Most probably, the temperature of the pressurizing fixing rollerwithout a heat source is lower than that of the heated portion. However, the heated portiondoes not contact the pressurizing fixing rollerand is not cooled by it.

62 62 62 1 h 62 62 2 12 FIG.C 12 FIG.D h (4) Then, the transport fixing beltis driven to start idling rotation in the forward direction (see) and is stopped when the heated portionhas reached the second position P(see). In the lower belt portion of the transport fixing belt, when the transport fixing belthas stopped moving, the heated portionextends to the outside of the contact area CN by the distance indicated by the distance information J.

62 2 1 62 2 2 62 61 63 62 64 63 h h h h In the upper belt portion, the heated portionis moved in the forward direction by the distance indicated by the distance information J, which is smaller than that of the distance information J, and is then stopped. The heated portionremains at the second position Pand does not reach the cooling area CA beyond the second position P. The heated portionis moved while contacting the heating fixing rollerbut separating from the pressurizing fixing roller. The heated portionis thus cooled neither by the cooling unitnor the pressurizing fixing roller.

62 62 2 62 61 h c 62 62 1 c 12 FIG.C (5) Then, the transport fixing beltis driven to perform idling rotation in the reverse direction and is stopped when the cooled portionhas reached the first position P(see). In the lower belt portion of the transport fixing belt, the heated portionwhich extends to the outside of the contact area CN is moved in the forward direction by the distance indicated by the distance information J. Meanwhile, the cooled portiondoes not reach the contact area CN and is thus prevented from cooling the heating fixing roller.

62 61 63 62 62 61 h c 12 FIG.D 150 62 1 2 62 (6) In this manner, thereafter, as illustrated in, the control devicedrives the transport fixing beltto repeatedly perform forward and reverse idling rotation by using the first position Pand the second position Pas the reference positions to stop the transport fixing belt. The heated portionis moved while contacting the heating fixing rollerbut separating from the pressurizing fixing roller. The cooled portionof the transport fixing beltdoes not contact the heating fixing roller.

62 64 63 62 62 62 62 61 62 62 61 h c h During this idling rotation of the transport fixing belt, neither of the cooling unitnor the pressurizing fixing rollercools the heated portionof the transport fixing belt. Nor does the cooled portionof the transport fixing belttouch the heating fixing roller. Hence, the temperature of the heated portionof the transport fixing beltis not unnecessarily lowered by the heating fixing roller.

62 63 60 (7) When the standby mode is canceled, the pressurizing fixing rolleris shifted to the contact position, and then, the second fixing unitis returned to the regular operation mode. Forward and reverse idling rotation of the transport fixing beltis repeatedly performed until the standby mode is canceled, as in the first exemplary embodiment.

62 1 2 62 1 3 In the second exemplary embodiment, forward and reverse idling rotation of the transport fixing beltduring the standby mode is performed based on the first position Pand the second position Pas the reference positions to stop the transport fixing belt. However, as in the modified example of the first exemplary embodiment, the first position Pand the third position Pmay be used as the reference positions.

In a first example, the second fixing unit of the first exemplary embodiment is realized, and a series of drive control processing is executed for the second fixing unit during the standby mode.

In the first example, when heating power to the heating fixing roller is interrupted, the transport fixing belt of the second fixing unit performs idling rotation in the forward and reverse directions within a predetermined range.

In the first example, the transport fixing belt is driven to perform forward and reverse idling rotation in a cycle of two to five seconds such that a heated portion of the transport fixing belt contacts the heating fixing roller.

In a first comparative example, a second fixing unit similarly configured to that of the first example is realized. When heating power to the heating fixing roller is interrupted, the transport fixing belt of this second fixing unit performs idling rotation only in the forward direction.

A series of drive control processing is executed for the second fixing unit of the first example and that of the first comparative example during the standby mode under the following conditions.

The second fixing units of the first example and the first comparative example are started (warmed-up) first, and then, the first fixing units are started. While the first fixing units are being started, the supply of heating power to the second fixing units is interrupted (no power is supplied), and then, the second fixing units are shifted to the standby mode.

13 FIG.A It is now assumed that the initial temperature of the heating fixing roller to perform a fixing operation is set to 140° C., and then, the supply of heating power to the heating fixing roller is interrupted, and the second fixing units are shifted to the standby mode. The relationship between the wait time (selected in a range of 60 seconds) after the supply of heating power is interrupted and the temperature change of the heating fixing roller is examined, and the results shown inare obtained.

13 FIG.B As illustrated in, the temperature drop of the heating fixing roller of the first example is 2.5° C. after a wait time of 10 seconds and is 9.0° C. after a wait time of 30 seconds.

In contrast, the temperature drop of the heating fixing roller of the first comparative example is 9.5° C. after a wait time of 10 seconds and is 22.5° C. after a wait time of 30 seconds.

It is thus validated that the second fixing unit of the first example can contain a temperature drop to be smaller than that of the first comparative example.

The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.

(((1)))

a heating fixing unit that is rotatable and includes a heat source; a belt-like transport fixing unit that is rotatably provided as a result of being tightly stretched on the heating fixing unit and that transports a medium having an unfixed image formed thereon while contacting a surface of the medium on which the unfixed image is formed; a pressurizing fixing unit that is rotatable and is disposed to face the heating fixing unit so as to sandwich the transport fixing unit therebetween and that applies pressure so as to form a fixing area between the pressurizing fixing unit and the heating fixing unit, the fixing area being an area where the unfixed image is fixed; a cooling unit that cools the transport fixing unit, the cooling unit being disposed in a transport region of the transport fixing unit for the medium so as to contact a back side of the transport fixing unit, the cooling unit being disposed at a position farther downstream than the fixing area in a transport direction of the medium; and a driving controller that executes drive control during a standby mode to cause the transport fixing unit to perform idling rotation to repeat a forward rotation operation and a reverse rotation operation so that a portion of the transport fixing unit including a contact area where the transport fixing unit contacts the heating fixing unit and an area of the transport fixing unit which has been heated by the heating fixing unit and which has not yet reached a cooling area of the cooling unit contacts the heating fixing unit, the standby mode being a mode in which power supply to the heat source of the heating fixing unit is interrupted or reduced.(((2))) A fixing device comprising:

The fixing device according to (((1))), wherein, during the standby mode, the driving controller stops the forward rotation operation of the transport fixing unit and causes the transport fixing unit to start the idling rotation to perform the reverse rotation operation.

(((3)))

The fixing device according to (((2))), wherein, after the transport fixing unit starts the idling rotation to perform the reverse rotation operation, the driving controller stops driving the transport fixing unit when a cooled portion of the transport fixing unit cooled by the cooling unit has reached a first position, the first position being a position at which the cooled portion of the transport fixing unit has not yet reached the contact area, and the driving controller then causes the transport fixing unit to start the idling rotation to perform the forward rotation operation.

(((4)))

The fixing device according to claim (((3))), wherein, after the transport fixing unit starts the idling rotation to perform the forward rotation operation, the driving controller stops driving the transport fixing unit when a heated portion of the transport fixing unit has reached a second position, the second position being a position at which the heated portion of the transport fixing unit has not yet reached a cooling area of the cooling unit, and the driving controller then causes the transport fixing unit to start the idling rotation to perform the reverse rotation operation, and thereafter, the driving controller causes the transport fixing unit to perform the idling rotation to repeat the forward rotation operation and the reverse rotation operation between the first position and the second position.

(((5)))

The fixing device according to (((3))), wherein, after the transport fixing unit starts the idling rotation to perform the forward rotation operation, the driving controller stops driving the transport fixing unit when the cooled portion of the transport fixing unit has reached a third position, the third position being a position at which the cooled portion of the transport fixing unit has not yet reached the contact area, and the driving controller then causes the transport fixing unit to start the idling rotation to perform the reverse rotation operation, and thereafter, the driving controller causes the transport fixing unit to perform the idling rotation to repeat the forward rotation operation and the reverse rotation operation between the first position and the third position.

(((6)))

The fixing device according to one of (((1))) to (((5))), wherein the driving controller causes the transport fixing unit to perform the idling rotation to repeat the forward rotation operation and the reverse rotation operation so that a portion of the transport fixing unit which is passing through the cooling area of the cooling unit and a portion of the transport fixing unit which has passed through the cooling unit do not reach the contact area.

(((7)))

The fixing device according to (((6))), wherein the driving controller causes the transport fixing unit to perform the idling rotation to repeat the forward rotation operation and the reverse rotation operation so that a heated portion of the transport fixing unit heated by the heating fixing unit does not reach the cooling area of the cooling unit.

(((8)))

The fixing device according to one of (((1))) to (((7))), wherein the pressurizing fixing unit includes a contacting/separating unit that shifts the pressurizing fixing unit from a contact position to a non-contact position during the standby mode, the contact position being a position at which the pressurizing fixing unit contacts the transport fixing unit, the non-contact position being a position at which the pressurizing fixing unit is separated from the transport fixing unit.

(((9)))

The fixing device according to (((8))), wherein the pressurizing fixing unit does not include a heat source.

(((10)))

a position detector that is disposed on a farther upstream side than the fixing area in the transport direction of the medium and detects a position of a leading end or a trailing end of the medium in the transport direction of the medium, wherein, based on a detection result of the position detector, the standby mode is canceled and power supply to the heat source of the heating fixing unit is started.(((11))) The fixing device according to one of (((1))) to (((9))), further comprising:

an image forming unit that forms an unfixed image on a medium; and the fixing device according to one of (((1))) to (((10))) that fixes the unfixed image formed on the medium onto the medium. An image forming system comprising: